Within the field of data communication and radio communications, the technology known as “spread spectrum” is often employed in order to make a deterministic-signal appear stochastic. Such a signal will be similar to white noise, thus making it very difficult to understand an intercepted signal. Furthermore, it may also be used when trying to suppress fading.
One known method for achieving “spread spectrum” is fast frequency hopping. The frequency employed at any given moment in such a system is determined by a random frequency generator comprising a PRN, which is driven by a synchronization signal known both a receiver and transmitter, in order to enable the receiver to “follow” the frequencies used by the transmitter
In the field of random number generators it is known a number of techniques to generate a random number or signal. Examples of PRNs are ML-sequencer; and Linear Congurential Generators (LCG); and More General Congurence (MGC); and Prime Modulus LCG (PMMLCG).
A conventional binary PRN, such as the ML-sequencer, comprises in its simplest form a shift register which has feed back signals from two or more sockets at predetermined positions from the register. The feed back signals are added to each other and then fed back to the register.
Another conventionally PRN, such as the Linear Congurential Generators (LCG) or the More General Congurence (MGC) or the Prime Modulus LCG (PMMLCG), is driven by an input signal. The output signal is fed back to the PRN and used for further generation of the random number signal.
Common for all above mentioned PRNs are that they are strongly dependent on its previous state, which has the disadvantage that a disturbance in a signal in the PRN will propagate in the PRN and give rise to fault propagation.
Such fault propagation may cause a serious error in a one way communication system comprising a sender and a receiver. The PRN is here used to generate a scrambled signal that must be correct in order for the receiver to be able to unscramble the signal and retract important information that can be relied upon without confirmation to the sender.
Furthermore, it has long been known a PRN with feed forward control using the so called Tiny Encryption Algorithm by David Wheeler and Roger Needham. However, this PRN uses a great number of addition operators and XOR operators in order to achieve a result matching the PRN using signal feed back as mentioned above. The known forward control PRN uses too many operators for the system to be cost efficient both regarding manufacturing and regarding energy consumption. The many operators may also be too complex for the PRN to be implemented in system using the above spread spectrum.
Therefore, there is a long felt need for an improved PRN with no fault propagation and minimised number of operators.